Fuel cell assembly fluid flow plate having conductive fibers and rigidizing material therein

ABSTRACT

A fluid flow plate is preferably formed with three initial sections, for instance, two layers of conductive (e.g., metal) fibers and a barrier material (e.g., metal foil) which is interposed between the two layers. For example, sintering of these three sections can provide electrical path(s) between outer faces of the two layers. Then, the sintered sections can be, for instance, placed in a mold for forming of flow channel(s) into one or more of the outer faces. Next, rigidizing material (e.g., resin) can be injected into the mold, for example, to fill and/or seal space(s) about a conductive matrix of the electrical path(s). Preferably, abrading of surface(s) of the outer face(s) serves to expose electrical contact(s) to the electrical path(s).

STATEMENT OF GOVERNMENT RIGHTS

The Government of the United States of America has rights in thisinvention pursuant to Contract No. DE-AC02-94CE50389 awarded by the U.S.Department of Energy.

TECHNICAL FIELD

This invention relates, generally, to fuel cell assemblies and, moreparticularly, to construction of fluid flow plates for fuel cellassemblies.

BACKGROUND ART

Fuel cells electrochemically convert fuels and oxidants to electricity,and fuel cells can be categorized according to the type of electrolyte(e.g., solid oxide, molten carbonate, alkaline, phosphoric acid, orsolid polymer) used to accommodate ion transfer during operation.Moreover, fuel cell assemblies can be employed in many (e.g., automotiveto aerospace to industrial) environments, for multiple applications.

A Proton Exchange Membrane (hereinafter "PEM") fuel cell converts thechemical energy of fuels such as hydrogen and oxidants such asair/oxygen directly into electrical energy. The PEM is a solid polymerelectrolyte that permits the passage of protons (i.e., H⁺ ions) from the"anode" side of a fuel cell to the "cathode" side of the fuel cell whilepreventing passage therethrough of reactant fluids (e.g., hydrogen andair/oxygen gases). Some artisans consider the acronym "PEM" to represent"Polymer Electrolyte Membrane." The direction, from anode to cathode, offlow of protons serves as the basis for labeling an "anode" side and a"cathode" side of every layer in the fuel cell, and in the fuel cellassembly or stack.

Usually, an individual PEM-type fuel cell has multiple, generallytransversely extending layers assembled in a longitudinal direction. Inthe typical fuel cell assembly or stack, all layers which extend to theperiphery of the fuel cells have holes therethrough for alignment andformation of fluid manifolds that generally service fluids for thestack. As is known in the art, some of the fluid manifolds distributefuel (e.g., hydrogen) and oxidant (e.g., air/oxygen) to, and removeunused fuel and oxidant as well as product water from, fluid flow plateswhich serve as flow field plates of each fuel cell. Also, other fluidmanifolds circulate coolant (e.g., water) for cooling.

As is known in the art, the PEM can work more effectively if it is wet.Conversely, once any area of the PEM dries out, the fuel cell does notgenerate any product water in that area because the electrochemicalreaction there stops. Undesirably, this drying out can progressivelymarch across the PEM until the fuel cell fails completely. So, the fueland oxidant fed to each fuel cell are usually humidified. Furthermore, acooling mechanism is commonly employed for removal of heat generatedduring operation of the fuel cells.

Flow field plates are commonly produced by any of a variety ofprocesses. One plate construction technique, which may be referred to as"monolithic" style, compresses carbon powder into a coherent mass. Next,the coherent mass is subjected to high temperature processes which bindthe carbon particles together, and convert a portion of the mass intographite for improved electrical conductivity. Then, the mass is cutinto slices, which are formed into the flow field plates. Usually, eachflow field plate is subjected to a sealing process (e.g., resinimpregnation) in order to decrease gas permeation therethrough andreduce the risk of uncontrolled reactions. Typically, flow fieldchannels are engraved or milled into a face of the rigid,resin-impregnated graphite plate. Undesirably, permeability of thegraphite and machining processes therefor limit reduction of platethickness. So, one is disadvantageously limited from increasing thenumber of corresponding fuel cells which occupy a particular volume in afuel cell stack, and which can contribute to overall power (voltage,current) generation. Moreover, resin-impregnated graphite plates aresusceptible to brittle failure and expensive in terms of cost of rawmaterials, as well as time for processing and tool wear in machining.

Another known configuration for a flow field plate embosses at least oneflow field channel into a laminated assembly of compressible,electrically conductive sheets (i.e., graphite foil). The flow fieldplate has two outer layers of compressible, conductive sheet materialand a center metal sheet interposed therebetween. The exterior surfacesof each of the two compressible outer layers constitute two major facesfor the flow field plate. A flow field channel is embossed into at leastone of these major faces. Such a design is disclosed in U.S. Pat. No.5,527,363 to Wilkinson et al. (entitled "Method of Fabricating anEmbossed Fluid Flow Field Plate," issued Jun. 18, 1996, and assigned toBallard Power Systems Incorporated and Daimler-Benz AG) and U.S. Pat.No. 5,521,018 to Wilkinson et al. (entitled "Embossed Fluid Flow FieldPlate for Electrochemical Fuel Cells," issued May 28, 1996, and assignedto Ballard Power Systems Incorporated and Daimler-Benz AG). Ashortcoming of this design is the lack of a stable, integrated, metallicconduction path between the major faces. A further shortcoming is theinability to withstand extra compression without deformation,degradation, or flattening of the flow channel.

Thus, a need exists for easy formation of a fluid flow plate havingenhanced toughness and satisfactory conductivity, strength, and sealingproperties. A further need exists for such a fluid flow plate in whichflow channels thereof can withstand increased compressive force in afuel cell stack. In particular, a need exists for the fluid flow plateto maintain its shape so greater compressive loads can be applied to thefuel cell stack to compress gas diffusion layers adjacent to the plate,for advantageous savings of space.

SUMMARY OF THE INVENTION

Pursuant to the present invention, shortcomings of the existing art areovercome and additional advantages are provided through the provision ofa fluid flow plate having conductive fibers and rigidizing material. Theconductive fibers are formed into electrical path(s) extendingeffectively in parallel with a longitudinal axis of a fuel cell assemblythat includes the fluid flow plate, which extends generally transverselywith respect to the longitudinal axis. The conductive fibers are locatedin a section of the fluid flow plate. The conductive fibers havespace(s) therebetween. The electrical path(s) are adapted to conductelectrical current generated by the fuel cell assembly. A portion of therigidizing material is positioned in at least one of the space(s). Therigidizing material has a relatively low density. The section of thefluid flow plate includes a flow channel adapted to service fluid(s) forthe fuel cell assembly.

In one aspect of the invention, the conductive fibers can be joinedand/or sintered to form the electrical path(s). The electrical path(s)can resemble a conductive matrix. The conductive fibers can comprisemetal (e.g., stainless steel), and the conductive fibers can bemetallurgically bonded to form the electrical path(s).

The section of the fluid flow plate can include electrical contact(s) tothe electrical path(s). The rigidizing material can have a relativelylow fluid permeability. A quantity of the rigidizing material can filland/or seal at least one of the space(s). The rigidizing material caninclude plastic resin. A number of the conductive fibers can be shapedand/or embossed for formation of the flow channel. A part of therigidizing material can form the flow channel.

The fluid(s) can include reactant gas for a fuel cell of the fuel cellassembly. The fuel cell can comprise a PEM-type fuel cell. The sectionof the fluid flow plate can include substantially parallel and/orgenerally serpentine flow channels.

In another aspect of the invention, a fluid flow plate includes firstconductive fibers, second conductive fibers, barrier material, andrigidizing material. The first and second conductive fibers are locatedin respective first and second sections of the fluid flow plate, whichextends generally transversely with respect to a longitudinal axis of afuel cell assembly that includes the fluid flow plate. The first andsecond sections of the fluid flow plate extend generally transversely atrespective first and second positions along the longitudinal axis. Thefirst conductive fibers have first space(s) therebetween. The secondconductive fibers have second space(s) therebetween. The conductivebarrier material is interposed between the first and second sections ofthe fluid flow plate. The first and second conductive fibers and theconductive barrier material form electrical path(s) extendingeffectively in parallel with the longitudinal axis. A first portion ofthe rigidizing material is positioned in at least one of the firstspace(s). A second portion of the rigidizing material is positioned inat least one of the second space(s). The rigidizing material has arelatively low density. The first and/or second section(s) of the fluidflow plate include a flow channel adapted to service fluid(s) for thefuel cell assembly.

In yet another aspect of the present invention, the first and secondconductive fibers and the conductive barrier material can be joinedand/or sintered to form the electrical path(s). The electrical path(s)can resemble a conductive matrix. The first and second conductive fiberscan comprise metal, the barrier material can comprise metal foil, andthe first and second conductive fibers and the barrier material can bemetallurgically bonded to form the electrical path(s).

The first section of the fluid flow plate can include first electricalcontact(s) to the electrical path(s). The second section of the fluidflow plate can include second electrical contact(s) to the electricalpath(s). A first quantity of the rigidizing material can fill and/orseal at least one of the first space(s). A second quantity of therigidizing material can fill and/or seal at least one of the secondspace(s). The first section of the fluid flow plate can include the flowchannel, and a number of the first conductive fibers can be shapedand/or embossed for formation of the flow channel.

The invention further contemplates a process for constructing a fluidflow plate. First and second conductive fibers are located in respectivefirst and second sections for the fluid flow plate. The first and secondsections extend generally transversely at respective first and secondpositions along a longitudinal axis. The first and second conductivefibers have respective first and second space(s) therebetween.Conductive barrier material is interposed between the first and secondsections. The first and second conductive fibers and the conductivebarrier material are formed into electrical path(s) extendingeffectively in parallel with the longitudinal axis. A first portion ofrigidizing material is positioned in at least one of the first space(s).A second portion of the rigidizing material is positioned in at leastone of the second space(s). The rigidizing material has a relatively lowdensity. A flow channel is formed in the first and/or second section(s).

In a further aspect of the invention, the flow channel can be formedthrough shaping and/or embossing the first and/or second section(s), andmolding a part of the rigidizing material. A surface of the rigidizingmaterial can be abraded to expose electrical contact(s) to theelectrical path(s).

Thus, the present invention advantageously provides a simpleconstruction for a fluid flow plate that is light-weight, conductive,tough, and considerably resistant to compression. In particular, thefluid flow plate can be a fiber-reinforced composite.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter which is regarded as the invention is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other objects, features, andadvantages of the invention will be readily understood from thefollowing detailed description of preferred embodiments taken inconjunction with the accompanying drawings in which:

FIG. 1 is a sectional, elevation, side view of one example of a fuelcell assembly incorporating and using the fluid flow plate(s) of thepresent invention;

FIG. 2 is a plan view of an outer face of one example of a fluid flowplate of the fuel cell assembly of FIG. 1;

FIG. 3 is a cutaway, sectional, partial, side representation of fluidflow plates serving as flow field plates in a fuel cell of the fuel cellassembly of FIG. 1, in accordance with the principles of the presentinvention;

FIG. 4 is a cutaway, sectional, partial, side representation of twoouter layers and a barrier layer interposed therebetween prepared to beformed into a fluid flow plate, illustrating the layers as forming aconductive matrix, in accordance with the principles of the presentinvention; and

FIG. 5 is a cutaway, sectional, partial, side representation of thelayers of FIG. 4 nearly formed into a fluid flow plate, illustratingflow channels formed into each outer layer by a mold and rigidizingmaterial positioned in spaces about the conductive matrix, in accordancewith the principles of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

In accordance with the principles of the present invention, a fuel cellassembly is provided in which a fluid flow plate has conductive fibersformed into continuous electrical path(s) extending between two outerfaces of the fluid flow plate. The electrical path(s) form a conductivematrix, with space(s) thereabout filled and/or sealed with rigidizingmaterial. The outer face(s) of the fluid flow plate have flow channelsformed thereon. Further, surfaces of the outer face(s) of the fluid flowplate are abraded to expose electrical contacts to the underlyingelectrical path(s).

An example of a fuel cell assembly incorporating and using the novelfeatures of the present invention is depicted in FIG. 1 and described indetail herein.

In this exemplary embodiment, a fuel cell assembly 100 includes endplates 102 and 104, insulation layers 106 and 108, and currentcollector/conductor plates 110 and 112, with a working section 114therebetween. Further, the working section includes one or more activesections and can include a selected number of cooling sections, as willbe understood by those skilled in the art. Also, a number of structuralmembers 116 join the end plates, as is known in the art.

Working section 114 includes a number of layers 118. The layersgenerally form fluid manifolds 150 for supplying fluids to, removingfluids from, and otherwise communicating and/or servicing fluids asdesired within the working section, as will be appreciated by thoseskilled in the art. The layers of fuel cell assembly 100 might haveapplied thereto compressive forces equivalent to approximately twohundred to four hundred pounds per square inch over the majority ofsurface of fluid flow plate 200 (FIG. 2).

Preferably, a plurality of layers 118 form one or more (e.g., onehundred and eight) PEM-type fuel cells 300 (FIG. 3). The constructionand utilization of PEM fuel cells is known in the art. By connecting anexternal load (not shown) between electrical contacts (not shown) ofcurrent collector/conductor plates 110 and 112, one can complete acircuit for use of current generated by the one or more PEM-type fuelcells.

One example of a layer 118 of working section 114 is depicted in FIG. 2as fluid flow plate 200. The plate has a fluid flow face 202 with aplurality of substantially parallel and generally serpentine flowchannels 204 thereon. The flow channels receive and transmit one or morefluids through ports 206 and 208 which are in fluid communication withcorresponding fluid manifolds 150 and 150'. For instance, the flowchannels can include respective inlets 206 and outlets 208 in fluidcommunication with corresponding entry and exit fluid manifolds 150 and150'.

As will be understood by those skilled in the art, a given fluid flowplate 200 may be a bipolar, monopolar, combined monopolar (e.g., anodecooler or cathode cooler), or cooling plate. In one example, fluid flowplate 200 serves as a flow field plate and flow channels 204 conductfluid which includes reactant fluid for fuel cell assembly 100. Thereactant fluid serves as fuel or oxidant for a given fuel cell 300 (FIG.3). For instance, the flow channels can carry reactant gas (e.g., a fuelsuch as hydrogen or an oxidant such as air/oxygen) as well as liquid(e.g., humidification and/or product water), as will be understood bythose skilled in the art.

A typical fluid flow plate 200 (FIG. 2) might have dimensions of 8.0 to10.0 in. height and 7.0 to 9.0 in. width. Further, the thickness of thefluid flow plate is preferably in the range 0.05 to 0.12 in., and ismost preferably in the range 0.055 to 0.070 in. Also, a given flowchannel 204 (FIGS. 3 and 5) on face 202 might have cross-sectionaldimensions of 0.04 to 0.06 in. width and 0.025 to 0.050 in. depth.

Referring to FIG. 2, fluid flow plate 200 has a number of peripheralholes 210 therethrough, which can cooperate in formation of fluidmanifolds of fuel cell assembly 100. In one embodiment, portions of theperipheral holes are defined by arcs or rims 212 that are fixed,attached, or connected to the fluid flow plate. These rims can have anydesired number of components and can be formed, for example, from thesame fiber-reinforced composite which forms the fluid flow plate, orfrom material such as molded plastic or elastomer. Preferably, theperimeters of layers 118 are formed with minimal amounts of materialdisposed generally transversely beyond the active extent of workingsection 114 as well as the fluid manifolds of fuel cell assembly 100, asrepresented in FIG. 2.

As will be understood by those skilled in the art, gasketing material orgaskets 304, 304' (FIG. 3) seal peripheral holes 210 and cooperate withthe longitudinal extents of layers 118 in formation of the fluidmanifolds. A given gasket 304, 304' might take the form of, forinstance, a frame gasket made from a polytetrafluoroethylene ("PTFE")material manufactured by E. I. DuPont de Nemours Company and sold underthe trademark TEFLON®. Alternatively, multiple O-ring gaskets might beused.

For purposes of illustration, FIG. 3 depicts fuel cell 300 with fluidflow plates 200, 200' serving as flow field plates. In particular, flowfield plate 200 might serve as an anode side of the fuel cell, and flowfield plate 200' might serve as a cathode side of the fuel cell. Thatis, face 202 might be an anode face, and face 202' might be a cathodeface. For instance, flow channels 204 might carry hydrogen, as fuel, andhumidification water. Further, flow channels 204' might carryair/oxygen, as oxidant, as well as humidification water and/or productwater, as will be understood by those skilled in the art.

Fuel cell 300 includes membrane or solid electrolyte 306. Preferably,solid electrolyte 306 is a solid polymer electrolyte made using apolymer such as a material manufactured by E. I. DuPont de NemoursCompany and sold under the trademark NAFION®. Further, an activeelectrolyte such as sulfonic acid groups might be included in thispolymer. In another example, the solid polymer electrolyte might beformed from a product manufactured by W. L. Gore & Associates (Elkton,Md.) and sold under the trademark GORE-SELECT®. Moreover, catalysts 308and 308' (e.g., platinum), which facilitate chemical reactions, areapplied to the anode and cathode sides, respectively, of the solidpolymer electrolyte. This unit can be referred to as a "membraneelectrode assembly" (hereinafter "MEA") 310. The MEA might be formedfrom a product manufactured by W. L. Gore & Associates and sold underthe trade designation PRIMEA 5510-HS.

MEA 310 is sandwiched between anode and cathode gas diffusion layers(hereinafter "GDLs") 312 and 312', respectively, which can be formedfrom a resilient and conductive material such as carbon fabric or carbonfiber paper. In one embodiment of a gas diffusion layer 312, 312',porous carbon cloth or paper is infused with a slurry of carbon blackand sintered with TEFLON® material. The anode and cathode GDLs serve aselectrochemical conductors between catalyzed sites of solid polymerelectrolyte 306 and the fuel (e.g., hydrogen) and oxidant (e.g.,air/oxygen) which each flow in anode and cathode flow channels 204 and204', respectively. Further, the GDLs also present to the surfaces ofthe MEA a combination of microscopic porosity and macroscopic porosity.Microscopic porosity allows reactant gas molecules to pass generallylongitudinally from the flow channels to a surface of the MEA.Macroscopic porosity allows product water formed at the cathode surfaceof the MEA to be removed therefrom by flowing generally longitudinallyinto the cathode flow channels, to prevent flooding of the catalystparticles.

In one example, water having a pH value of approximately five might beadded to a given reactant gas stream conducted by flow channels 204,204'. The water would desirably serve to humidify membrane 306.

FIG. 4 depicts first and second outer sections or layers 400, 402 andbarrier material or layer 404 interposed therebetween. Furthermore, thelayers 400, 402, 404 form a number of electrical paths represented byexemplary conductive web or matrix 406, as detailed herein. Outer layers400, 402 include conductive fibers 408. For example, each outer layer400, 402 may comprise a stainless steel wool blanket initially having athickness preferably in the range 0.18 to 0.38 in., and most preferablyequal to approximately 0.25 in. In another example, layer(s) 400, 402might include chopped metal fiber. The barrier layer 404 may comprise,for instance, stainless steel foil initially having a thicknesspreferably in the range 0.001 to 0.005 in., and most preferably in therange 0.001 to 0.003 in. As detailed herein with respect to FIG. 5,layers 400, 402, 404 are formed, assembled, joined or combined intofluid flow plate 200.

In one example, an outer layer 400, 402 might be formed from a productmanufactured by Bekaert Fiber Technologies (Marietta, Ga.) and soldunder the trademark BEKIPOR® WB. Further, barrier layer 404 might beformed, for instance, from stainless steel foil available commerciallyfrom Ulbrich Stainless Steels and Special Metals, Inc. (North Haven,Conn.).

Conductive matrix 406 may be formed, for example, by sintering of layers400, 402, 404. For instance, the layers 400, 402, 404 may be heated in avacuum, or a container of protective gas (e.g., hydrogen), to asintering temperature, that is, a temperature at which conductive fibers408 metallurgically bond to each other as well as to barrier layer 404,thereby creating continuous electrical paths in conductive matrix 406between outer surfaces 410 and 412 of the respective outer layers 400and 402.

Referring to FIG. 5, (e.g., sintered) layers 400, 402, 404 may be placedin a mold 550 (e.g., a molding die or a forming die), which preferablyincludes first and second forming portions 552 and 552'. The first andsecond forming portions serve to form flow channels 204 and 204' intocorresponding outer surfaces 410 and 412 that form respective fluid flowfaces 202 and 202' (FIG. 3).

A forming portion 552, 552' might be formed from any of a wide varietyof commercially available tool or die steels. In one example, a formingportion 552, 552' might be formed from an air hardening die steel knownin the trade as "A-2."

Referring to FIG. 5, mold 550 preferably includes roundish protuberances554, 554' which serve to form flow channels 204, 204', respectively.Namely, the roundish protuberances, upon closing of forming portions 552and 552' toward each other with layers 400, 402, 404 positionedtherebetween, serve to guide conductive fibers 408 which are disposedobliquely with respect to the protuberances into forming and/orsupporting lands 504, 504', respectively.

As depicted in FIG. 5 for purposes of illustration, protuberances 554,554' might resemble semicircles in order to effect semicircular crosssections for flow channels 204, 204', respectively. In another example,the protuberances might resemble polygons, such as rectangles ortrapezoids, with a number of roundish "corners" in order to effect flowchannel cross sections having relatively flat bottoms with sloped,curved, or roundish connections to sidewalls preferably alignedgenerally orthogonally with respect to the bottom, as represented inFIG. 3. As illustrated in FIG. 5, the protuberances may have trunkswhich widen in connecting to the remainder of the mold, resulting inflow channels 204, 204' having widened mouths, which in turn may bemodified to any desired degree such as during abrasion of lands 504,504' to expose electrical contacts 506, 506' to conductive matrix 406,as discussed herein. As will be understood by those skilled in the art,numerous geometric variations for the protuberances and flow channelsare possible, in accordance with the principles of the presentinvention.

Referring still to FIG. 5, in one preferred embodiment of the presentinvention, after forming of flow channels 204, 204' and while layers400, 402, 404 are still in mold 550, rigidizing material 500 ispositioned in voids or spaces 502 about conductive matrix 406 byprocesses such as insert molding or resin transfer molding. Namely, therigidizing material can fill and/or seal some, many, or all of thespaces about the conductive matrix. In particular, certain space(s)could remain unfilled. That is, pocket(s) (e.g., of air) could remainbetween conductive fibers 408 of the conductive matrix 406, though suchpocket(s) are preferably surrounded and isolated by rigidizing material500.

Rigidizing material 500 may comprise, for instance, epoxy resin. In oneexample, the rigidizing material might be formed from a productmanufactured by Master Bond, Inc. (Hackensack, N.J.) and sold under thetrade designation EP29LPSP. Such resin systems typically have a densityof 1 to 2 grams per cubic centimeter (e.g., depending on whether afiller is used), and, for illustrative purposes, may be considered to besubstantially impermeable.

Furthermore, referring to FIGS. 3 and 5, abrading, sanding, or machiningof lands 504, 504' on respective fluid flow faces 202, 202' desirablyexposes electrical contact(s) 506, 506' to the underlying conductivematrix 406. That is, the conductive matrix and the contacts theretoadvantageously provide continuous electrical paths between the fluidflow faces of fluid flow plate 200. As illustrated in FIG. 3, theelectrical paths can be accessed by abutting GDLs 312, 312' through thecorresponding electrical contacts 506, 506' at the lands 504, 504'.Furthermore, on the non-abraded surfaces, rigidizing material 500 servesto isolate the conductive matrix from fluid carried in flow channels204, 204'.

In accordance with the present invention, barrier layer 404advantageously protects against leakage of (e.g., reactant) fluidbetween flow channels 204 and 204' on respective opposite faces 202 and202' of fluid flow plate 200. Desirably, the barrier layer 404 alsoprovides dimensional stability to outer layers 400, 402 while rigidizingmaterial 500 is positioned therein, as described above.

In an alternative embodiment of the present invention, a fluid flowplate 200 could omit barrier layer 404. Then, a single layer (e.g., anexpanded layer 400 or an expanded layer 402) of conductive fibers 408could be formed (e.g., sintered) into electrical paths for conductivematrix 406. Next, flow channels 204, 204' could be formed (e.g., shaped,embossed) onto respective fluid flow faces 202 and 202' of the fluidflow plate. Finally, rigidizing material 500 could be positioned inspaces about the conductive matrix. For purposes such as dimensionalstability and leakage prevention, the single layer may comprise astainless steel wool blanket initially having an approximate thicknessof 0.50 to 1.00 in. Further, following construction, this alternativefluid flow plate might have a thickness preferably in the range 0.04 to0.25 in., and most preferably in the range 0.06 to 0.12 in. That is,such an alternative fluid flow plate preferably has a relatively largerthickness than the fluid flow plate discussed above which includes thebarrier layer 404. In one aspect, the additional thickness serves toreduce the chance of reactant permeation through the fluid flow plate.

The subject invention can advantageously decrease weight as well as costof fluid flow plate 200 by including rigidizing (e.g., plastic resin)material 500 instead of conductive fibers (e.g., stainless steel) 408 orother conductive material, in space(s) 502 about conductive matrix 406.For instance, the fluid flow plate might have a volume which is at leasteighty percent non-conductive rigidizing material 500, with the balancecomprising the conductive fibers and optional filler.

By decreasing density of fluid flow plate 200 through inclusion ofrigidizing material 500 therein, one can desirably increase performanceof, for example, automobiles which employ fuel cell assembly 100. Thatis, lightening of the fuel cell assembly translates into less energyexpended in transporting the fuel cell assembly in order to gainoperational benefits of fuel cells 300. Those skilled in the art willappreciate the efficiencies possible from use of the present inventionin a wide range of vehicular and other desired applications.

Rigidizing material 500 desirably serves to provide structural rigidityand/or strength to fluid flow plate 200. In one aspect, the rigidizingmaterial fortifies or maintains the integrity of flow channels 204despite increased compression applied in a longitudinal direction offuel cell assembly 100. This longitudinal compression of the fluid flowplate and fuel cell stack 100 advantageously saves volume therein, ordecreases volume thereof, at a certain power output, that is, with acertain number of fuel cells 300. Moreover, such longitudinal stackcompression is advantageous to increase power output from a particularvolume of the stack, that is, by increasing the number of fuel cells 300in that particular volume. These and other advantages of the presentinvention will be appreciated by those skilled in the art.

In one aspect, flow channel(s) 204 may be formed with variable crosssection(s), in accordance with the principles of the subject invention.

For purposes of illustration, one can consider designs contrary to thepresent invention. Were one to omit rigidizing material 500 from aparticular fluid flow plate, then, at a certain compression level of thefuel cell stack, the particular fluid flow plate could render acorresponding fuel cell less effective or even inoperable due toflattening of flow channels. Namely, flattening of the flow channelsunder compression would restrict and/or choke off flow of reactant fluidflow (optionally including humidification fluid) or coolant for thecorresponding fuel cell. By including rigidizing material 500 in fluidflow plate 200, the present invention advantageously addresses suchproblems, as described herein.

A given fluid flow plate 200 which conducts fluids on both faces 202,202' might be configured so the fluids have, for example, parallel flowor counter flow among the various flow channels 204, 204'. Inparticular, a parallel flow configuration might generally transverselyalign flow on the opposing faces 202, 202' by positioning correspondingfirst and second inlets at opposite sides of a first corner of theplate, and corresponding first and second outlets at opposite sides of agenerally diametrically opposed second corner of the plate. Further, acounter flow design might provide flow in generally transverselyopposite directions on opposing faces 202, 202' by placing firstinlet(s) and second outlet(s) at opposite sides of a first corner of theplate, and first outlet(s) and second inlet(s), respectively, atopposite sides of a generally diametrically opposed second corner of theplate.

Operation of fuel cell assembly 100 can include periods or intervals ofaction and inaction, such as an active use followed by idling. Also, thefuel cell assembly can be employed for varied (e.g., automotive toaerospace to industrial) applications, in various environments.

Numerous alternative embodiments of the present invention exist. Fluidflow plate 200 and/or fluid manifold(s) 150, 150' could serve anydesired function in any position of fuel cell assembly 100. Further,fluid flow face 202 could easily have any number of flow channels 204.Any flow channel 204 could easily have any appropriate shape orstructure. Also, flow channels 204 could easily be configured todeviate, to any desired degree, from parallel alignment and/orserpentine design. Moreover, any of ports/inlets 206 and/orports/outlets 208 could employ any mechanism for fluid communicationbetween appropriate flow channel(s) 204 and fluid manifold(s) 150, 150'.Fluid flow plate may include parts other than layers 400, 402, 404 andrigidizing material 500. Design choices permit variation in constructiontechnique(s) and/or material(s) for any portion of fluid flow plate 200and/or fuel cell assembly 100. Furthermore, fluid flow plate(s) 200could easily be employed in any appropriate type(s) of fuel cell(s).Additionally, working section 114 could easily include any desiredtype(s) of fuel cell(s).

Although preferred embodiments have been depicted and described indetail herein, it will be apparent to those skilled in the relevant artthat various modifications, additions, substitutions and the like can bemade without departing from the spirit of the invention and these aretherefore considered to be within the scope of the invention as definedin the following claims.

What is claimed is:
 1. A fluid flow plate for a fuel cell assembly, saidfuel cell assembly having a longitudinal axis, said fluid flow plateextending generally transversely with respect to said longitudinal axis,said fluid flow plate comprising:a plurality of first conductive fiberslocated in a section of said fluid flow plate, said first conductivefibers having a number of spaces therebetween; a plurality of secondconductive fibers; metal foil located between said first conductivefibers and said second conductive fibers; said first and secondconductive fibers and said metal foil comprising at least one electricalpath extending effectively in parallel with said longitudinal axis, saidat least one electrical path adapted to conduct electrical currentgenerated by said fuel cell assembly; rigidizing material including aportion positioned in at least one of said spaces, said rigidizingmaterial having a relatively low density; and said section including aflow channel adapted to service at least one fluid for said fuel cellassembly.
 2. The fluid flow plate of claim 1, wherein said firstconductive fibers are at least one of joined and sintered for said atleast one electrical path.
 3. The fluid flow plate of claim 1, whereinsaid at least one electrical path comprises a conductive matrix.
 4. Thefluid flow plate of claim 1, wherein said first conductive fiberscomprise metal and said first conductive fibers are metallurgicallybonded for said at least one electrical path.
 5. The fluid flow plate ofclaim 4, wherein said metal comprising said first conductive fibersincludes stainless steel.
 6. The fluid flow plate of claim 1, whereinsaid section includes at least one electrical contact to said at leastone electrical path.
 7. The fluid flow plate of claim 1, wherein saidrigidizing material serves to decrease fluid permeability of said plate.8. The fluid flow plate of claim 1, wherein a quantity of saidrigidizing material at least one of fills and seals at least one of saidspaces.
 9. The fluid flow plate of claim 1, wherein said rigidizingmaterial includes plastic resin.
 10. The fluid flow plate of claim 1,wherein a number of said first conductive fibers are at least one ofshaped and embossed for formation of said flow channel.
 11. The fluidflow plate of claim 1, wherein a part of said rigidizing material formssaid flow channel.
 12. The fluid flow plate of claim 1, wherein said atleast one fluid includes reactant gas for a fuel cell of said fuel cellassembly.
 13. The fluid flow plate of claim 12, wherein said fuel cellcomprises a PEM fuel cell.
 14. The fluid flow plate of claim 1, whereinsaid section includes a plurality of flow channels which are at leastone of substantially parallel and generally serpentine.
 15. A fluid flowplate of a fuel cell assembly, said fuel cell assembly having alongitudinal axis, said fluid flow plate extending generallytransversely with respect to said longitudinal axis, said fluid flowplate comprising:a plurality of first conductive fibers located in afirst section extending generally transversely at a first position alongsaid longitudinal axis, said first conductive fibers having a number offirst spaces therebetween; a plurality of second conductive fiberslocated in a second section extending generally transversely at a secondposition along said longitudinal axis, said second conductive fibershaving a number of second spaces therebetween; metal foil interposedbetween said first and second sections; said first and second conductivefibers and said metal foil comprising at least one electrical pathextending effectively in parallel with said longitudinal axis;rigidizing material including first and second portions, said firstportion positioned in at least one of said first spaces, said secondportion positioned in at least one of said second spaces, saidrigidizing material having a relatively low density; and at least one ofsaid first and second sections including a flow channel adapted toservice at least one fluid for said fuel cell assembly.
 16. The fluidflow plate of claim 15, wherein said first and second conductive fibersand said metal foil are at least one of joined and sintered to form saidat least one electrical path.
 17. The fluid flow plate of claim 15,wherein said at least one electrical path comprises a conductive matrix.18. The fluid flow plate of claim 15, wherein said first and secondconductive fibers comprise metal, and wherein said first and secondconductive fibers and said metal foil are metallurgically bonded to formsaid at least one electrical path.
 19. The fluid flow plate of claim 15,wherein said first section includes at least one first electricalcontact to said at least one electrical path, wherein said secondsection includes at least one second electrical contact to said at leastone electrical path.
 20. The fluid flow plate of claim 15, wherein afirst quantity of said rigidizing material at least one of fills andseals at least one of said first spaces, wherein a second quantity ofsaid rigidizing material at least one of fills and seals at least one ofsaid second spaces.
 21. The fluid flow plate of claim 15, wherein saidfirst section includes said flow channel, wherein a number of said firstconductive fibers are at least one of shaped and embossed for formationof said flow channel.
 22. A process for constructing a fluid flow plate,said process comprising:locating a plurality of first conductive fibersin a first section for said fluid flow plate, said first sectionextending generally transversely at a first position along alongitudinal axis, said first conductive fibers having a number of firstspaces therebetween; locating a plurality of second conductive fibers ina second section for said fluid flow plate, said second sectionextending generally transversely at a second position along saidlongitudinal axis, said second conductive fibers having a number ofsecond spaces therebetween; interposing metal foil between said firstand second sections; forming said first and second conductive fibers andsaid metal foil into at least one electrical path extending effectivelyin parallel with said longitudinal axis; positioning a first portion ofrigidizing material in at least one of said first spaces, saidrigidizing material having a relatively low density; positioning asecond portion of said rigidizing material in at least one of saidsecond spaces; and forming a flow channel in at least one of said firstand second sections.
 23. The process of claim 22, wherein said formingof said flow channel includes at least one of shaping and embossing saidat least one of said first and second sections and molding a part ofsaid rigidizing material.
 24. The process of claim 22, furthercomprising the step of abrading a surface of said rigidizing material toexpose at least one electrical contact to said at least one electricalpath.